An optical navigation device, such as an optical mouse, typically includes an optical navigation sensor integrated circuit (IC) that functions as a miniature digital camera to continually collect images of a surface that the device is resting upon and to determine the speed and direction that the device is being moved across the surface by comparing sequentially recorded frames of image information. Image frames are collected at a very high rate, such as 1,500 image frames per second, and the resolution of the optical navigation sensor IC is high enough to detect very small movements of the device relative to the navigation surface.
Collecting image information from the navigation surface involves illuminating the navigation surface and focusing light that reflects off the navigation surface onto the optical navigation sensor IC. Typically, the optical navigation sensor IC, an illumination source, and an optical component such as a lens are integrated into a module that fixes the distance between the lens and the navigation surface at the focal length of the lens. Fixing the distance between the lens and the navigation surface at the focal length of the lens ensures that the collected image information is of sufficient quality for optical navigation.
In some applications, it is desirable to have a “thin” optical navigation device that can be, for example, placed into a slot of a laptop or hand-held computer for storage and/or charging. While current optical navigation devices work well, the size of the navigation device is a function of the focal length of the lens, which dictates the required distance between the lens and the navigation surface. In view of this, what is needed is a system for optical navigation that can collect image information sufficient for optical navigation and that is small enough for desired applications.